1. Field of the Invention
The present invention relates to a controller that performs torque control of a hydraulic pump for supplying hydraulic oil to a plurality of actuators and also relates to a work machine provided with the controller.
2. Description of the Background Art
Work machines have been known that include a variable displacement hydraulic pump driven by an engine and a plurality of actuators that are actuated by hydraulic oil supplied from the hydraulic pump.
In a work machine of this kind, the suction torque (torque) of the hydraulic pump is set based on an accelerator command or mode selection command input by the operator, and the tilt angle of the hydraulic pump is controlled so that the output of the hydraulic pump (sum total of outputs of hydraulic pumps when a plurality of hydraulic pumps are provided) does not exceed the suction torque.
However, where the suction torque is fixed to a constant value, the hydraulic pump output can, under certain operation conditions (a large load or combination of actuator operations), be set to be equal to or higher than the output that is actually necessary to actuate the actuators and the operation efficiency can decrease.
In order to resolve this problem, for example, Japanese Patent Application Laid-Open Nos. 2001-248186 and 2002-138965 disclose a configuration in which a discharge pressure of a hydraulic pump is detected and the suction torque of the hydraulic pump is regulated correspondingly to the value of the discharge pressure.
However, in order to control the speed of each actuator, throttles of M/I (meter-in) opening or M/O (meter-out) opening are provided in a hydraulic circuit, and the discharge pressure of the hydraulic pump that is demonstrated as a result of the throttling does not accurately correspond to the load necessary to actuate the actuators. The resultant problem is that when the suction torque of the hydraulic pump is set based on the discharge pressure of the hydraulic pump as in the configuration disclosed in Japanese Patent Application Laid-Open Nos. 2001-248186 and 2002-138965, a suction torque is set that exceeds the torque that is actually necessary for the actuators.
More specifically, for example, in a boom cylinder serving to raise and lower the boom of the work machine, although the discharge pressure of the hydraulic pump increases due to pressure loss in response to throttling in both the boom raising operation and the boom lowering operation, the suction torque that is actually necessary is large in the raising operation and small in the lowering operation. With the configuration disclosed in Japanese Patent Application Laid-Open Nos. 2001-248186 and 2002-138965, since the suction torque of the hydraulic pump is set correspondingly to the discharge pressure of the hydraulic pump, irrespectively of the operation contents, the suction torque of the hydraulic pump is also set higher than the output necessary to actuate the actuators.